1. Field of the Invention
The present invention relates to magnetic recording media, methods of manufacturing the same, magnetic medium substrates employed in the magnetic recording media, and magnetic storage units, and particularly to a magnetic medium substrate in which a carbon layer is formed on the surface of a pore of an anodic alumina film on a non-magnetic substrate, and a magnetic recording medium using the magnetic medium substrate, making it possible to increase capacity, increase speed, reduce cost, and ensure reliability.
There is a growing need for capacity increase, higher speed, and lower cost with respect to a recording medium used in external magnetic storage units for computers and household video storage devices due to a rapid increase in the amount of information stored therein. The principal emphasis for satisfying such a need is to increase the recording density of the magnetic recording medium. The conventionally mainstream in-plane recording method using a continuous magnetic film is approaching a technological limit on reaching a recording density of 100 Gbit/in2 because of a problem in that with an increase in recording density, signal-to-noise ratio decreases because of an increase in transition noise and the thermal stability of recorded magnetization decreases.
2. Description of the Related Art
In order to reduce transition noise, a patterned medium in which minute magnetic particles are wrapped in a non-magnetic film and arranged regularly has been actively studied as a new type of magnetic recording medium. In the patterned medium, the exchange interaction and the magnetostatic interaction between magnetic particles are interrupted by the non-magnetic film between the magnetic particles. Accordingly, it is possible to reduce transition noise. Further, the perpendicular recording method has attracted attention again as a method that can achieve recording densities higher than 1 Tbit/in2. As patterned media, those in which magnetic particles are self-organized and arranged (see Sun et al., Science, vol. 287, No. 17, pp. 1989 (2000), Japanese Laid-Open Patent Application No. 2000-48340, and Japanese Laid-Open Patent Application No. 2000-54012) and those using regular pores formed in an anodic alumina film have been presented. FIG. 1 is a sectional view of a conventional magnetic recording medium using an anodic alumina film. As shown in FIG. 1, a magnetic recording medium 100 is formed by filling pores 105 formed in an anodic alumina film 103 formed on a lower electrode layer 102 on a substrate 101 with a magnetic material 104 (see Japanese Laid-Open Patent Application No. 2002-175621). The anodic alumina film 103 can be obtained by anodizing an aluminum film in an oxalic acid aqueous solution. In doing so, the aluminum film is converted into an alumina film, and a pore is formed in the center of a hexagonal cell. The hexagonal cells are formed regularly. Therefore, it is expected that by filling the pores with a magnetic material, magnetic particles are arranged regularly and the exchange interaction and the magnetostatic interaction between the magnetic particles are interrupted by the alumina film, which is a non-magnetic film, thereby making it possible to greatly reduce transition noise.
By the way, in order to realize a highly reliable magnetic recording medium, high performance is required in terms of the tribology and the chemical stability of a magnetic head and the surface of the magnetic recording medium, for instance, the durability of the surface of the magnetic recording medium with respect to the sliding of the magnetic head and the corrosion resistance thereof to acids or alkalis resulting from a variety of contaminants.
For instance, the above-described magnetic recording medium 100 using the anodic alumina film 103 has a problem in terms of corrosion resistance. That is, the anodic alumina film is an amorphous alumina film, and is converted into a polycrystalline alumina film by heat treatment at temperatures higher than or equal to 850° C. The polycrystalline alumina film is stable with respect to acid or alkali, while it has been reported that the amorphous alumina film is gradually or rapidly dissolved by acids having a pH of 4.2 or lower or alkalis having a pH of 9.9 or higher (see P. P. Mardilovich et al., J. Membrane Science, 98, (1995) 143). A magnetic storage unit that contains a magnetic recording medium may be internally contaminated by various chemical substances in air or in the magnetic storage unit as impurity gases or liquid droplets, which may adhere to and corrode the magnetic recording medium. If corrosion occurs, the surface of the magnetic recording medium becomes uneven so that a magnetic head that floats as low as tens of nanometers above the surface of the magnetic recording medium suffers a head crash.
In light of the sliding of the magnetic head, normally, a lubricant having a main chain of perfluoropolyether is applied to reduce the coefficient of friction, and it functions as a cushioning material when the magnetic head comes into contact with the magnetic recording medium. In particular, the lubricant is scattered or dissolved and vaporized by the sliding of the magnetic head against the magnetic recording medium. Accordingly, in order to ensure long-time durability, it is important to store the lubricant sufficiently on the surface of the magnetic recording medium. However, the lubricant is prevented from being stored sufficiently on the above-described magnetic recording medium using the anodic alumina film because its surface is alumina oxide or metal. In general, in dealing with this, a protection layer of an amorphous carbon film or a DLC film is formed on the surface. However, mere provision of the protection layer does not provide sufficient durability against sliding.